All of them - depending on how much you lose to spillage. Like a bleach-based sanitizer, it won't lose effectiveness with multiple uses on clean surfaces. You could make a 5 or even 2.5 gallon batch, pour a half-gallon or so into the first bucket, swirl that bucket, pour that sanitizer into the next bucket then repeat. Line up all your buckets and you could have relatively quick work. There's no need to sanitize the outside of the bucket with a dip IMHO.